Production of paper



Dec. 26, 1967 lcLEBELT ETA'L 3,359,643

PRODUCTION OF PAPER Filed March 22, 1965 ive 730A;

am zwg United States Patent 3,359,643 PRODUCTION OF PAPER John C.Leihelt and Leslie F. Newby, Jr., Wisconsin Rapids, Wis; said Newbyassignor to Consolidated Papers, Inc., Wisconsin Rapids, Wis., acorporation of Wisconsin Filed Mar. 22, 1965, Ser. No. 441,579 9 Claims.(Cl. 34-25) This invention relates to the production of paper and moreparticularly to novel method and means for controlling the uniformity ofa newly formed paper web in a continuous papermaking process.

More specifically, the present invention relates to novel method andmeans for controlling the caliper (thickness) or variations in caliperacross the width of the traveling paper web, such as for examplereduction of hard and/ or soft spots, ridges, wavy edges, roughprintability due to corrugations in the cross or transverse direction ofthe sheet and similar roll defects, with the end in view of producingpaper of enhanced uniformity and thickness and concomitant physicalproperties such as uniform porosity, improved subsequent coating pickup,enhanced smoothness, opacity and print quality.

Non-uniformity of caliper has been particularly noticed in the newlyformed paper web after it leaves the first machine calender, thismachine calender comprising a plurality of vertically aligned steelrolls, the web passing through one or more pairs or nips of these rolls,which serve to density the web while hot just after it leaves the lastof the conventional series of drier drums but prior to coating andfurther calendering or supercalendering.

The newly formed paper web, which can have an average temperature on theorder of about 150-180 F. as it enters the first nip of the calenderstack, by heat transfer causes the steel rolls thereof to become heated,resulting in heat expansion of the calender rolls and bringing theperipheries of adjacent rolls closer to each other and causing enhanceddensification of the paper web. It is known, however, that the heatedrolls do not expand uniformly throughout their length resulting in a webbeing more highly densified in some areas than in others and as a matterof fact resulting very often in production of a series of transversecorrugations extending longitudinally of the paper web. Such irregularexpansion of the calender rolls can be minimized by subjecting undulyheated high spots to cooling, and conversely by subjecting relativelylow spots to heating to cause them to expand.

It has been found in accordance with the present invention that thecross direction temperature of the moving paper web entering theaforesaid machine calender stack can vary across the web while its crossdirection profile remains quite stable in the longitudinal or machinedirection of the paper. It is further found that temperature differencesin certain areas of the web could transfer to the steel rolls of thecalender stack thereby expanding these calender rolls in the areascorresponding to those of the higher paper temperature. In turn, theseexpanded areas of the calender rolls in the stack were found to thencompress the paper passing through it in the same areas of high papertemperature more than in the areas of lower paper temperature.Conversely, cooler paper areas could contract or diminish areas of thesecalender rolls and said areas would compress the paper passing throughto less than those areas of higher temperatures. It was furthermorefound that the cross direction caliper profile after or following thisfirst calender stack was inversely proportional to the cross directiontemperature profile of the paper entering the stack.

It was therefore found that in accordance with the present invention bythermally treating selected areas of the newly formed forwardly movingheat dried web prior to subjecting it to calenderin-g, that the effectsof the heat variations longitudinally of the rolls could be minimized.That is to say, by thermally treating selected areas of one or bothfaces of the heated web, such as by impinging, blowing or showering gas,for example air, against selected areas of the web in heat exchangerelationship correlated to the said expansion or lack of expansion, theeifeots of heat variations longitudinally of the rolls could beminimized and paper webs produced of more uniform cross directionalcaliper. For example, impinging cooled air at a given distance from amoving web of paper by means of a plurality of orifices or nozzlesdisposed transversely of the web and individually controllable, atransfer of heat from the moving web of paper and disruption of themoisture and heat laden layers of air which normally follow the movingweb, may be effected. This disruption and cooling effect of the air onthe paper web in turn causes the transfer of heat from the hotcalendering rolls to the cooler web causing the rolls to locally cooland decrease in diameter and thereby inversely increasing the caliper ofthe moving web in the selected areas in which the air was applied.

Of course, the reverse of the foregoing can also be done, either aloneor in combination with cooling air in adjacent areas, by the foregoingmeans to deliver relatively heated air to selected areas to therebyincrease the temperature of the moving web and thereby, in turn,increasing the temperature of the calendering rolls in these relatedareas. This in turn causes expansion of the calender rolls in selectedareas and as a result decreases caliper of the moving web in the thusexpanded areas.

It will thus be seen that the newly formed, dried paper web while stillwarm can display a relatively fixed or stable cross directiontemperature profile which it can transfer to the calender rolls of thefirst machine or calender stack disposed adjacent the last paper dryingdrum. This transfer temperature profile in turn can distort the calenderrolls by developing relatively expanded or contracted areas, dependentupon the temperature profile, which in turn can calender the paper webpassing through more or less strongly according to the roll areasinvolved. By employing the air showering method and means of thisinvention one can eliminate what has been found to be the main variable,and surprisingly the greatest contributor, of calender variations,namely that of paper web temperature differences in the cross ortransverse direction of the moving web. This air shower technique hasbeen found to provide a more rapid and sensitive control than hasheretofore been available and has provided means not only forcontrolling variable longitudinal expansion in the rolls after theirbeing heated but has also provided means to correct or compensate forvaria tions inherent in the rolls. As a result, air pipes directed ontothe rolls or heater strips on the rolls can very often be eliminated bydirecting relatively heated and/or relatively cooled air to selectedspots or areas of the forwardly moving paper web in a directiontransversely thereof.

The practice of the present invention can be employed in combinationwith and correlated to an on-the-machine traversing caliper instrumentsuch as described in the copending application of John B. Kahoun, Ser.No. 313,476, filed Oct. 3, 1963, in engagement with the paper web as itleaves the aforesaid calender stack to provide prompt and continuouscontrol of the paper caliper.

Other objects and advantages of the present invention, and the detailsof construction and arrangement of parts of the means for carrying outthe method thereof, will be apparent from a consideration of thefollowing specification and accompanying drawings, wherein FIG. 1 is adiagrammatic side elevational view of the arrangement of apparatus forcarrying out the present invention.

FIG. 2 is a fragmentary plan view thereof with the top calender rollremoved.

FIG. 3 is an enlarged fragmentary detail on the line 33 of FIG. 2,showing a solenoid valve actuated highpressure, low-volume air nozzle.

FIG. 4 is a plan view of a pair of optional low-pressure, high-volumeair nozzles.

FIG. 5 is a diagrammatic View of remote control means for operating theair shower nozzles disposed adjacent a thickness profile graph recorderwhereby the control means may be actuated in a manner correlated to thegraph.

Referring to the drawings, the reference numeral generally indicates amachine calender stack comprising a plurality of vertically alignedsteel rolls 11 through which the paper web 12 passes. The paper web maypass through a single nip, i.e., between an adjacent pair of rolls 11,11or may pass between a plurality of nips such as the five indicated inthe drawing.

The paper web leaves the last drying drum 13 at a temperature on theorder of about 220 F. and it approaches the stack at about the roll 14at a temperature on the order of ISO-180. The top roll temperature ofthe calender stack becomes heated by contact with the web to atemperature of about 160180 and the bottom roll temperature becomesheated to approximately 135- 145 F.

As previously explained, the web 12 as it leaves the last drier drum 13and enters the steel rolls of the calender stack 10 has been found to beheated to varying degrees in a transverse direction, thereby causing therolls 11 of the calender stack-to be non-uniformly expanded in alongitudinal direction, resulting in non-uniform density of the issuingweb after it leaves the calender.

In accordance with the present invention this difference in density isminimized by showering as desired cooling or heating gas, preferablyair, against selected areas of one or both faces of the moving web justbefore it enters the calender stack 10. For this purpose, a plurality ofnozzles 15 are disposed in a series extending transversely of the weband in a direction parallel thereto, these nozzles 15 being connected toa header or common supply source of gas or air 16 suspended andsupported in suitable manner as by the means 17. These nozzles 15 can beadapted to direct a compressed gas such as air essentially at highpressure and low volume a given distance above the moving web of paperso that the gas may cool by expansion and cool the web by transfer ofheat from the paper to the roll and by disruption of the heat andmoisture-laden boundry layers of air which normally follow the movingweb. In the alternative, nozzles 18 may be employed to deliver a highvolume of cooled gas, i.e., air. at a low-pressure from a suitablesource directed through the nozzles disposed at a given distance fromthe moving web of paper. Again, the combined low tempera ture plus highvelocity air promotes a transfer of heat from the web of paper anddisrupts the moisture and heatla'den layers. of air which normallyfollow the moving web.

These nozzles are provided with suitable valve means such as ball valvesas at 19 which may be provided with manual control means 20 or byremote-controlled solenoid means 21, individually controllable by, forexample, the control buttons 22, on the panel 23. One or more of thesevalves may be actuated to deliver relatively cool or relatively heatedair correlated to the high or low spots on the paper web to provide theeffects previously described. This operation may be conveniently carriedout in correlation to the caliper gauge means generally indicated as 24which engages and traverses the web 12 as it leaves the calender stack10 and provides a thickness profile graph 25 by means of an x-yrecorder. Thus, where low spots are shown on the graph 25 a suitablevalve 19 may be actuated either by means of the manual lever 20 or byremote-controlled buttons 22, to cool the web at the areas conforming tothe low spots on the graph 25 thereby cooling the web and thus providingless heat to be transferred to the rolls 11 reducing their expansion, orconversely delivering heated air to areas of the web corresponding tothe high spots on the graph 25 thereby to transfer heat to the rolls 11to a degree substantially equal to adjacent areas whereby to induceexpansion of the rolls at such areas and to minimize differences inexpansion of the roll longitudinally thereof and to consequently providea web of enhanced uniform thickness in its transverse direction, and tothus provide an improvement in the quality of the paper which issubsequently coated and further calendered or supercalendered.

Although we have shown and described the preferred method and means ofour invention, it will be understood by those skilled in the art thatchanges may be made in the details thereof without departing from theirscope as comprehended by the following claims.

We claim:

1. In a papermaking process wherein a newly formed, forwardly moving,heat dried web is subjected to densification between metalliccalendering rolls while retaining heat in varying degree transversely ofthe web, and wherein heat is transferred from said web to said rollsresulting in variable expansion longitudinally of said rolls, theimprovement which comprises thermally treating selected areas on atleast one face of said heated web by blowing gas thereagainst in heatexchange relationship correlated to said expansion whereby to minimizeexpansion variation prior to calendering thereof, by blowing relativelycool air against a portion of the web which is at a relatively highertemperature than other portions of the web and by blowing relativelywarm air against a portion of the web which is at a relatively lowertemperature than other portions of the web whereby to minimize theeffects of said heat variations longitudinally of said rolls.

2. In a papermaking process wherein a newly formed, forwardly moving,heat dried web is subjected to densification between metalliccalendering rolls while retaining heat in varying degree transversely ofthe web, and wherein heat is transferred from said web to said rollsresulting in variable expansion longitudinally of said rolls, theimprovement which comprises thermally treating selected areas of saidheated web, prior to calendering thereof by blowing relative cool airagainst a portion of the web which is at relatively higher temperaturethan other portions of the web, whereby to minimize the effects of saidheat variations longitudinally of said rolls.

3. In a paperrnaking process wherein a newly formed, forwardly moving,heat dried web is subjected to densification between metalliccalendering rolls While retaining heat in varying degree transversely ofthe web, and wherein heat is transferred from said web to said rollsresulting in variable expansion longitudinally of said rolls, theimprovement which comprises thermally treating selected areas of saidheated web, prior to calendering thereof by blowing relatively warm airagainst a portion of the web which is at a relatively lower temperaturethan other portions of the web whereby to minimize the effects of saidheat variations longitudinally of said rolls.

4. In a papermaking process wherein a newly formed, forwardly moving,heat dried web is subjected to densification between metalliccalendering rolls while retaining heat in varying degree transversely ofthe web, and wherein heat is transferred from said Web to said rollsresulting in variable expansion longitudinally of said rolls, theimprovement which comprises periodically calipering said web in atransverse direction as it leaves said calendering rolls and thermallytreating selected areas of said heated web, prior to calendering thereofby blowing streams of air thereagainst at temperatures inverselyproportional to the thickness of the web as determined by saidcalipering,

whereby to minimize the effects of said heat variations longitudinallyof said rolls.

5. In a papermak-ing apparatus comprising metallic calendering rollsdisposed adjacent the last paper drying drum wherein a newly formed,forwardly moving, dried web is subjected to densification between saidcalendering rolls while retaining heat in varying degree transversely ofthe web, and wherein heat is transferred from said web to said rollsresulting in variable expansion longitudinally of said rolls, means forthermally treating selected areas of said heated web, prior tocalendering thereof, whereby to minimize the effects of said heatvariations longitudinally of said rolls.

6. In a papermaking apparatus comprising metallic calendering rollsdisposed adjacent the last paper drying drum wherein a newly formed,forwardly moving, dried web is subjected to densification between saidcalendering rolls while retaining heat in varying degree transversely ofthe web, and wherein heat is transferred from said web to said rollsresulting in variable expansion longitudinally of said rolls, meanscomprising a series of selectively actuatable air jets disposed adjacentand parallel to said rolls for thermally treating selected areas of saidheated web, prior to calendering thereof, whereby to minimize theeffects of said heat variations longitudinally of said rolls.

7. In a papermaking apparatus comprising metallic calendering rollsdisposed adjacent the last paper drying drum wherein a newly formed,forwardly moving, dried web is subjected to densification between saidcalendering rolls while retaining heat in varying degree transversely ofthe web, and wherein heat is transferred from said Web to said rollsresulting in variable expansion longitudinally of said rolls, means forthermally treating selected areas of said heated web, prior tocalendering thereof, comprising a series of selectively actuatable airjets disposed between and parallel to said drying drum and calenderingrolls and adjacent to at least one web surface, whereby to minimize theeifects of said heat variations longitudinally of said rolls.

8. In a papermaking apparatus comprising metallic calendering rollsdisposed adjacent the last paper drying drum wherein a newly formed,forwardly moving, dried web is subjected to densification between saidcalendering rolls while retaining heat in varying degree transversely ofthe web, and wherein heat is transferred from said web to said rollsresulting in variable expansion longitudinally of said rolls, means forthermally treating selected areas of said heated web, prior tocalendering thereof, comprising a series of selectively actuatable airjets disposed between and parallel to said drying drum and calenderingrolls and adjacent to at least one web surface, and remote control meansfor said jets, whereby to minimize the effects of said heat variationslongitudinally of said rolls.

9. In a papermaking apparatus comprising metallic calendering rollsdisposed adjacent the last paper drying drum wherein a newly formed,forwardly moving, dried web is subjected to densification between saidcalendering rolls while retaining heat in varying degree transversely ofthe web, and wherein heat is transferred from said web to said rollsresulting in variable expansion longitudinally of said rolls,transversably reciprocable calipering means embracing said web disposedafter passage of the web through said cellular rolls, and means forthermally treating selected areas of said heated web by blowing streamsof air thereagainst at temperatures inversely proportional to thethickness of said web as determined by said calipering means comprisinga series of selectively actuatable air jets disposed between andparallel to said drying drum and calendering rolls and adjacent to atleast one web surface, pr-ior to calendering thereof, whereby tominimize the efiects of said heat variations longitudinally of saidrolls.

References Cited UNITED STATES PATENTS 2,012,115 8/1935 Woodruff 34160 X2,091,805 8/1937 Chuse 34-18 X 2,370,811 3/1945 Osgood 34 160 X3,071,865 1/1963 Faeber 34 31 X 3,161,482 12/1964 Gschwind et al.

OTHER REFERENCES Paper Trade Journal, Lockwood Trade Journal Co., Inc.,New York, June 10, 1963, pages -43.

KENNETH W. SPRAGUE, Primary Examiner.

1. IN A PAPERMAKING PROCESS WHEREIN A NEWLY FORMED, FORWARDLY MOVING,HEAT DRIED WEB IS SUBJECTED TO DENSIFICATION BETWEEN METALLICCALLENDERING ROLLS WHILE RETAINING HEAT IN VARYING DEGREE TRANSVERSELYOF THE WEB, AND WHEREIN HEAT IS TRANSFERRED FROM SAID WEB TO SAID ROLLSRESULTING IN VARIABLE EXPANSION LONGITUDINALLY OF SAID ROLLS, THEIMPROVEMENT WHICH COMPRISES THERMALLY TREATING SELECTED AREAS ON ATLEAST ONE FACE OF SAID HEATED WEB BY BLOWING GAS THEREAGAINST IN HEATEXCHANGE RELATIONSHIP CORRELATED TO SAID EXPANSION WHEREBY TO MINIMZEEXPAN-